1. Field of the Invention
The present invention relates to a gas-supplying apparatus, gas-supplying mechanism, and a gas supplying process in fuel cell, which can make use of heat in an effective manner by carrying out heat-exchange between a supply gas supplied into a fuel cell and an exhaust gas exhausted from the fuel cell.
2. Description of Related Arts
A fuel cell (solid macromolecular type fuel cell) has recently drawn considerable attention as a power source of an electric vehicle etc., because of its cleanness and excellent energy efficiency. Since the fuel cell works at a temperature above the room temperature, a supply gas to be supplied to the fuel cell is heated and the heat from an exhaust gas exhausted from the fuel cell is recovered. For example, Japanese Patent Laid-Open No. 7-176313 discloses a fuel cell system having a regenerative heat-exchanging apparatus, which carries out heat exchange between air supplied to the fuel cell (supply air) and exhaust air from the fuel cell, and which humidifies the supply air. According to the publication, the heat generated from the fuel cell can be effectively used.
However, in order to improve the efficiency of the fuel cell, much more effective utilization of the heat from the fuel cell has been desired. Also, it has been desired for effectively operating the fuel cell to vary, and preferably control, the temperature of the supply gas to be supplied to the fuel cell. In this case, it is preferred if the effective utilization of the heat and the temperature control of the supply gas can be realized with a simple configuration.
In addition, in a fuel cell system having a configuration that the supply gas is compressed through a compressor, and the compressed gas is supplied to the fuel cell, the supply gas is compressed only in a low amount through the compressor when the load of the fuel cell is small and; therefore, the temperature of the supply gas is small. Accordingly, the heat exchanger should heat the supply gas in this case. On the other hand, since the supply gas is heavily compressed when the fuel cell is heavily loaded, the temperature of the supply gas becomes large. In some cases, the temperature of the supply gas becomes higher than the operation temperature of the fuel cell (greater than 120° C.). Consequently, the heat exchanger should heat or cool down the supply gas, resulting in a complication of the apparatus. For this reason, it has been desired to develop a gas-supplying apparatus, which can control the temperature of the gas supplied to the fuel cell with a simple configuration.